This application requests support to study the effects of the ratio levels of dietary unsaturated/saturated fatty acids (U/S) on the life span of rats and on several of the basic morphologic and biochemical changes of aging in brain, heart and liver. Six different diets will be offered ad libitum to Wistar male rats. The ratio levels of U/S in the diets are 0.10, 1.5 and 13.5.- The levels of alpha-tocopherol are 2 mg and 200 mg %. To study the effect of the diets on the life span of the rats the diet will be offered from weaning to death. Mean and maximum life span will be established and the possible cause of death will be determined by complete autopsy. To study the effects of the diets on some of the morphologic and biochemical parameters of aging the rats will be offered the diets from weaning, but members of the different groups will be killed at 3,6,12,18,24,30 and 36 months after the initiation of the experiment when samples of blood (to determine levels of lipids and vit. E), brain, heart and liver will be obtained. The tissues will be stereologically analyzed by fluorescent, conventional light and electron microscopy to determine the fractional cytoplasmic volume of aging pigment (lipofuscin) in neurons, myocardial fibers and hepatocytes; the number and volume of the "parenchymal cells" per unit volume of tissue and their differential fractional volume and number in relation to "stromal elements" as well as the number and fractional cytoplasmic volume of nuclei, mitochondria, peroxisomes, residual bodies and rough and smooth endoplasmic reticulum. Biochemically the tissues will be analyzed to determine their content of vit. E, DNA, RNA, protein, lipids, water, glycogen, collagen, a series of enzymatic activities as well as the eventual occurrence of lipoperoxidation. Comparisons and correlations will be explored between morphologic and biochemical parameters, and between these parameters with age and with diet.